In general, inkjet printers include at least one printhead that ejects drops of liquid ink onto a surface of an image receiving member. In an indirect or offset printer, the inkjets eject ink onto the surface of a rotating image receiving member, such as a rotating metal drum or endless belt, before the ink image is transferred to print media. In a direct printer, the inkjets eject ink directly onto print media, which may be in sheet or continuous web form. A phase change inkjet printer employs phase change inks that are solid at ambient temperature, but transition to a liquid phase at an elevated temperature. Once the melted ink is ejected onto the media or image receiving member, depending upon the type of printer, the ink droplets quickly solidify to form an ink image.
Inkjet printers are used to print a wide range of documents using various types and colors of ink. Some printed documents are read by both humans and machines. For example, a check includes printed text that is both human readable and readable by automated check processing equipment. Check processing machines use Magnetic Ink Character Recognition (MICR) to identify printed characters in a check, such as routing and account numbers, quickly and accurately. The magnetic ink readable by MICR machines includes a suspension of magnetic particles, such as iron oxide, which are detectable using a magnetic field. The use of MICR printing is widespread and enables automated processing of checks and other documents even when the printed magnetic ink characters are visually obscured by stamps or other overprinting. Automated check processing machines perform high-speed character recognition using printed magnetic ink characters to identify account and routing numbers. While check processing is one application of magnetic ink printing, magnetic inks can be incorporated in a wide range of printed documents and can be used in conjunction with non-magnetic inks as well.
One challenge in using magnetic inks with inkjet printers relates to cleaning the magnetic inks from a printhead. Printers typically conduct various maintenance operations to ensure proper operation of the inkjets in each printhead. One known maintenance operation removes particles or other contaminants that may interfere with printing operations from each printhead in a printer. During such a cleaning maintenance operation, the printheads purge ink through some or all of the inkjets in the printhead. The purged ink flows from inkjet apertures located in a faceplate of each printhead onto the faceplate. The ink rolls downwardly under the influence of gravity to an ink drip bib mounted at the lower edge of the faceplate. The bib is configured with one or more drip points where the liquid ink collects and drips into an ink receptacle. In some printers, one or more wipers are manipulated to contact the faceplate of each printhead and wipe the purged ink toward the drip bib to facilitate the collection and removal of the purged ink.
While existing cleaning processes are useful to maintain printheads, removing residual purged ink from the printhead remains a challenge. This challenge is particularly significant in phase change magnetic ink printers since the ink in these printers can solidify and adhere to structures in the printer. Furthermore, magnetic inks contain small, very hard magnetite particles. Mechanical wiping of the printheads to remove purged ink can cause these particles to scratch the printhead face. Thus, improved cleaning of printheads that eject magnetic ink is desirable.